Small animals, as opposed to puppies and kittens, are delivered by courier service just like any other package — even though it is illegal to transport a live animal in this way in China, and despite the risks to the animal's life.

Sugar gliders, a tiny marsupial familiar to many Australians, are one of the most popular exotic pets that can be bought online and delivered by post in China.

The online demand for gliders in China has increased in part due to the popular video sharing platform TikTok, where users have posted videos of their pets jumping off high ledges and gliding into their hands.

But the safe delivery of small pets like gliders is not guaranteed, and some customers have posted negative reviews online claiming their new pet arrived dead in the box, or passed away within days of delivery.

"The deaths were a result of the long period in transit or they were thrown around during transportation," one pet vendor told the ABC.

The vendor, who declined to give his real name but uses the name Daosheng Pet Supplies Store on JD.com, tells his customers to film themselves opening their deliveries, in order to claim a refund if the animal inside has died.

"It would be difficult to breathe, difficult to thermoregulate, and it doesn't look like they have any water."

Beyond the risk of death from this mode of transportation, the animals could face lifelong psychological damage.

"It's one thing that you might be able to get an animal to survive a journey like that, it's a whole other thing to say it hasn't been affected by it … mentally, that animal would be very stressed out " Dr Orr said.

China's postal law states it is forbidden to post and deliver live animals, or insert them into postal materials.

However, customer-submitted photos posted on JD.com indicate that several major Chinese courier companies, including Yunda, ZTO and YTO, have been transporting parcels containing pets.

The ABC approached those three companies for comment but did not receive a response prior to publication.

In a statement, a JD.com spokesperson said the company was aware of concerns about the transportation of pets through its platform, and was looking into the issue.

"While all merchants on JD.com are required to be licensed and to operate in accordance with Chinese regulations, the company is looking into the standards of its merchants and their carriers in relation to the sourcing and transportation of pets," the spokesperson said.

Taobao, which is owned by Chinese e-commerce giant Alibaba, was also approached for comment.

Pets delivered in Australia too — but not in the post

Classifieds website Gumtree hosts thousands of listings for pets, with some breeders also offering to organise delivery for puppies and kittens, sometimes through the use of pet transportation companies.

eBay does not allow live animals to be listed on its site, and Facebook has also banned live animals on its Marketplace feature — but there are still plenty of pages and groups on the site where animals are advertised, with some also offering delivery.

But Dr Orr warned against choosing to have a puppy or kitten delivered, which can make it harder for new owners to know the animal did not come from a puppy farm, or whether the sale is a scam.

"Sometimes people forget that animals are not the same as any other commercial goods … the circumstances they're raised in directly impacts their long-term health and welfare and state of mind," she said.

"Convenience is a great thing if you want to buy cheap clothes online, but I think we have to be really careful how we trade pets online, to make sure that convenience doesn't compromise their welfare."

The RSPCA is today releasing new guidelines for the online advertising of pets, which are aimed at helping retailers better protect animals in line with the expectations of customers.

They include a range of requirements for those looking to sell animals online, as well as new due diligence measures for websites.

Red flags to look out for online:

If the seller is offering a puppy or kitten that is less than eight weeks old, they shouldn't be trusted: "The animal won't be fully weaned yet, or properly socialised," Dr Orr said.

If the seller says they "can arrange transportation", that's another warning sign: "They probably don't want you to come and see where the animal was bred, and that could be because they have really poor conditions, or they're a puppy farmer, or all sorts of reasons."

Some of those measures would require site owners to audit advertisements for blacklisted words like "dog fighting", and display a "report animal welfare concern" button on all animal advertisements.

"That's a bit of a disappointment, seeing as we have been working with industry on them, but we are hopeful that the online retailers will choose to comply.

"For some of these retailers, the pets category is one of their highest traffic areas … but they have a responsibility at the same time to make sure that those animals are safe, and they're not put in danger by being sold online."

In a statement, a Gumtree spokesperson said animal welfare is a top priority and the website has worked with the community and animal welfare agencies to improve its pets category over the past few years.

"Our commitment to animal welfare was also the reason why Gumtree actively worked with the RSPCA earlier this year to help develop their new guidelines for the online advertising of pets," the spokesperson said.

"We currently meet the vast majority of the requirements and will continue to roll out improvements to the category."